Alone in second at 6-under was England's Justin Rose, who came into this event looking to take over the top spot on the Sunshine (Southern Africa) Tour's Order of Merit.
Rose, who was born in South Africa and raised there until the age of 5, claimed his first professional title in his native Johannesburg three weeks ago at the Dunhill Championship, a tournament co-sanctioned by the Sunshine and European Tours.
The 21-year-old Rose currently stands third on the Sunshine Tour's money list with $112,803 (1,296,105 rand), behind South Africans Tim Clark ($125,744) and Retief Goosen ($118,796).
Clark, the winner of last month's South African Open at Durban Country Club, posted an even-par 70 in Thursday's first round. U.S. Open champion Goosen is taking some time off after winning the Johnnie Walker Classic in Australia and the Dimension Data Pro-Am in South Africa in consecutive weeks.
Rose took the clubhouse lead with a 64 in wet and windy morning conditions. He collected four birdies in five holes around the turn before taking a bogey at the 14th hole, then finished well with three straight birdies from the 15th.
His final birdie came when he chipped in from off the back of the green at the par-3 17th.
'I stole a shot from the course there,' Rose said. 'It was difficult to keep your rhythm out there with the rain coming and going. One minute you have your wet gear on, then you've got to take it off again. It was a tricky day.'
Moore, a 25-year-old South African from Port Elizabeth, pushed past Rose with a bogey-free round that included four birdies over the last six holes.
'I was really solid out there,' said Moore, the 1996 South African Amateur champion. 'I kept it in play and made a few nice putts.'
Moore's front nine was highlighted by a two-putt birdie at the par-5 seveth that was set up by a driver off the tee followed by a driver off the deck. He rolled in a 40-foot birdie at the final hole to secure a two-shot advantage heading into round two.
South Africans held five of the next six spots on the leaderboard. Mark Murless and Warren Abery shared third place with 5-under 65s, while Michael Green, Richard Sterne and Ian Palmer each shot 66 to finish alongside Englishman Benn Barham at 4-under.
Last year's winner, Mark McNulty of Zimbabwe, was forced to withdraw from the tournament Wednesday because of the flu.
Full-field scores from the Nashua Masters